A suicide bomber has struck at a wake in Yemen's southern city of Jaar, killing at least 45 people and wounding dozens more, the defence ministry said, in the deadliest attack since the army declared victory over Islamist militants in June.

Islamist group Ansar al-Sharia claimed responsibility for Sunday’s attack, which targeted a group of tribal fighters in revenge for their alliance with the Yemeni army during an offensive against militants in the southern province of Abyan.

"That was a preliminary operation. The next one will be bigger," a man who identified himself as a spokesman for Ansar al-Sharia told Reuters by telephone.

The attack highlighted the enduring threat of Islamist militancy in Yemen and may alarm the United States and Saudi Arabia, which increasingly view the impoverished state as a frontline in their war on al Qaeda and its affiliates.

Yemen is home to al Qaeda in the Arabian Peninsula, which US officials have described as the most dangerous offshoot of the global militant network.

A local official said charred bodies were strewn around the site of the blast, which wounded Abdul Latif Al Sayed, the leader of tribal fighting units known as Popular Committees, who has survived previous assassination attempts.

Two of his brothers were killed in the explosion.

"This cowardly act will not frighten us," said Saleh al-Sayed, a fellow tribal fighter and family member of the wounded leader. "We will fight the partisans of evil until the last man and the last breath."

Further east, in the province of Hadramout, a US drone fired on a vehicle carrying suspected militants, killing its three passengers, a local official said.

Ansar al-Sharia (Partisans of Islamic Law) seized several towns in Abyan last year, establishing a foothold there while then-President Ali Abdullah Saleh was grappling with mass protests that eventually toppled him.

The United States supported the Yemeni military campaign in which the army regained control of territory it had lost, but residents and analysts say the militants are simply lying low and waiting for a chance to regroup.

"A number of individuals from these gangs took refuge in the mountains next to the north of Jaar after the big defeat they were dealt by the army and Popular Committees," said state news agency Saba. "Today they resume their cowardly suicide operations."

Despite losing their territorial base, militants have shown they still pose a considerable threat, assassinating a southern military commander, and last week killing four policemen in an attack on Jaar police station.